Try running a2jmidid with pw-jack a2jmidid first — that bridges ALSA MIDI to JACK MIDI, and then use pw-link or qpwgraph to connect your app's MIDI input to the resulting Midi-Bridge ports
As amazingfate (the Armbian dev for this device) clearly stated on the forum: cellular and camera are not working, only display, touch, wifi, and bluetooth are functional—so it won't replace your phone OS for calls and texts
that’s a super specific and annoying issue! It sounds like Armbian is still exposing an A2DP (audio) profile even after you tweaked the main.conf. Have you tried disabling the audio sink entirely via Bluetooth CLI or modifying the /etc/bluetooth/audio.conf (if it exists) to set AutoConnect=false under [General]?